SOLUTION: it says find Sn for each arithmetic series described. a1=20, an=112, d=4. how do i find it ?

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Question 209963: it says find Sn for each arithmetic series described. a1=20, an=112, d=4. how do i find it ?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
it says find Sn for each arithmetic series described. a1=20, an=112, d=4. how do i find it ?
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S(n) is the sum of n terms of the series.
The formula is S(n) = (n/2)(a(1)+a(n))
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You need to find "n"
a(n) = a(1)+(n-1)d
112 = 20 + (n-1)*4
92 = (n-1)4
n-1 = 23
n = 24
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So you are looking for the sum of the 1st 24 terms of the series.
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Use the formula to get: S(24) = (24/2)(20+112) = 12*132 = 1584
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Cheers,
Stan H.
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